The present invention concerns a process for determining the pivot center of proximal and intermediary articulations, also known as joints, of an appendicular skeleton.
The appendicular skeleton comprises arms and legs and includes the proximal articulations of those limbs (i.e., hips and shoulders) and the intermediary articulations (i.e., elbows or knees) and distal articulations (wrists or ankles). The articulations are connected by proximal bone segments (humerus for arms or femur for legs) and distal bone segments (radius for arms or tibia for legs).
It is common for appendicular joints to be replaced with prosthetic devices. During such replacements, it is very important that the joint be properly alignedxe2x80x94a misaligned bone can shorten the lifespan of the replacement joint considerably, for example, as much as by 20% to 50% of the time. Proper alignment using traditional methods requires a significant amount of skill and experience.
During a surgery involving part of the appendicular skeleton, it is important for proper alignment to know the pivot centers of the proximal and intermediary articulations of the skeleton. In fact, when it is necessary to cut the proximal bone segment, for instance, it is important to make the cut exactly at a right angle with respect to the plane connecting these two articulations, or pivot centers. It is also useful to optimize pivot centers of articulations for physical therapy applications, and for sports medicine applications. Determining the pivot point can also be used as a diagnostic tool for tracking the progression of certain bone diseases.
In the case of the hip, for instance, the pivot center corresponds to the articulation center of the hip, which is spherical. This is not the case with a non-spherical articulation, such as, for example, the knee. The pivot center of the knee, for instance, corresponds to the average of a range of points (the xe2x80x9ccloud pointxe2x80x9d) formed by the pivot centers of this non-spherical articulation during the relative movement of the bone segments surrounding it.
Initially, articulations were positioned by observation. This method resulted in a relatively high failure rate, leading to the development of .mechanically assisted methods, such as those reported in the prior art, such as, for instance, the method disclosed by F. Leitner, F. Picard, R. Minfelde et al., Computer-Assisted Surgical Total Replacement of the Knee (published in the Proceedings of the First Joint Conference, Computer Vision, Virtual Reality and Robotics in Medicine, Medical Robotics and Computer Assisted Surgery (1997); and as published by S. L. Delp, et al., Computer Assisted Knee Replacement, Clinical Orthopedics and Related Research, 354, 49-56 (1998). Throughout these methods, a set of data are generated which, when analyzed, provides assistance in locating the ideal pivot point. Prior art techniques for generating data include preoperative imagery, where the pivot point is determined prior to surgery. This method, however, is somewhat complicated and requires sophisticated imaging equipment and technicians, and sometimes engineers. In general, traditional techniques used to generate these data remain somewhat rudimentary, and inaccuracies in these data generation techniques create inaccuracies in the pivot points generated even by computer-assisted techniques.
One improvement to traditional pre-surgical determinations of the pivot point utilizes at least four individual markers (optical-type, super-resonant, magnetic or inertial) which are surgically screwed into the bones, and each of which each is associated to a means of detection, such as a camera connected to a computer. This allows the medical staff to monitor the positioning and orientation of each marker in real time during a surgical procedure. For purposes of this invention, positioning is the x, y and z cartesian coordinates of the marker, and orientation is the polar coordinates of this marker, expressed at the point of reference point.
A When using this prior art method on a leg, for instance, the first two markers are affixed on either side of the knee, at the extremities toward the tibia and the femur. Two additional markers are affixed on the pelvis and a foot bone, respectively. The patient is placed horizontally, with his femur raised and restrained from movement, and then the tibia is moved toward the motionless femur. A computer is used during this movement to determine the maximal invariancy point, which corresponds to the pivot center of the knee articulation. The pivot center of the hip articulation may be determined in the same manner by moving the femur toward the trunk, and the pivot center of the ankle articulation by moving the foot toward the tibia
This solution has certain drawbacks. It requires a large number of markers, and since each marker must be attached to the corresponding bone, it is necessary to affix with screws at least some of these markers to the bone in question. These affixing procedures are time-consuming and can be rather traumatizing for the patient. Also, many methods of moving the body to collect data points for determining the pivot point are used, with differing outcomes. Lastly, differences in bone structure between patients make standardization of traditional techniques for locating optimal pivot points difficult.
Thus, it would be useful to have an optimized positioning method for use with computer assisted orthopedic surgery, which would provide accurately and reliably provide data for generating an optimal articulation pivot point, and which would be faster and less traumatizing for the patient than traditional methods of determining an optimal pivot point. It would also be advantageous to develop a standard technique which could be used for any bone structure and which could account for a wide variety of bone deformities.
The present invention overcomes these drawbacks, in that it provides a means for determining the pivot center of an articulation using only a single marker.
It is an object of the present invention to provide a method for optimizing the alignment of orthopedic prosthetic devices.
It is a further object of the invention to provide a method of generating data points from physical movements for use in determining the optimal pivot point of a bone articulation that is more accurate and reproduceable than prior art methods.
It is yet another object of the invention to provide a method for determining an optimal pivot point that is fast and less traumatic to the patient as compared to prior art methods.
It is another object of the invention to provide an optimal movement sequence for generating data points which can be used to reliably and accurately locate optimal pivot points of articulations.
It is also an object of the invention to locate an optimal pivot point using a single marker.
In this regard, the invention is a method for determining pivot centers for the proximal and intermediary articulations of an appendicular skeleton, for use during computer-assisted orthopedic surgery or other diagnostic or rehabilitative treatments. The novel method of the invention requires the affixation of a single marker to the bone, which may be affixed by screws or by less traumatic methods such as but not limited to external affixation devices such as elastic bands. Pivot centers for proximal and intermediary articulations may be determined through the use of at least one marker placed between intermediary and distal joints, and pivot centers for intermediary and distal articulations may be determined through the use of at least one marker placed over or at least near the distal joint.
Once the marker is affixed to the bone, the pivot center is determined using rotational movements of the appendicular skeleton in accordance with the sequence of the invention. The sequence of the invention utilizes at least the first and second rotations of the proximal bone segment around the proximal articulation in accordance with the first and second axes, sensibly orthogonal to each other, and at least the third and fourth rotations of the distal bone segment around the intermediary articulation, along the third and fourth axes, sensibly orthogonal to each other.
During the movement sequence, data points on the position and orientation of the marker are collected on a continuous basis from a predetermined point of reference, the localizer. Next, from among the resulting data collected on a continuous basis, a minimal number of distinct postures of the skeleton during the movement sequence are selected, and to each posture is ascribed a value representing the position and orientation of the marker in the predetermined point of reference. Next, from all of the values the coordinates of the optimal pivot point. (also called rotational center) of the proximal and intermediary articulations is determined. Once the optimal pivot points are determined, the optimal alignment of the articulations are possible. xe2x80x9cPatientxe2x80x9d as used herein denotes legged mammals, most particularly people although it is contemplated and within the scope of the present invention that the methods disclosed herein would work with other legged mammals as well.